The instant invention relates to an optical path folding system and more particularly to an adjustment device for such a system utilizing a pair of mirrors forming an acute angle therebetween for compact packaging of scanning devices or line imaging optical systems incorporating a charge coupled device (CCD) sensor.
Specifically, there is a class of optical scanners that incorporates the source material supported by a transparent platen in the proximity of a moving carriage caused to traverse in a path parallel to the platen and source material. By a combination of optical and electronic means the image of the source material may be dissected, converted into a train of electronic pulses, and reconstructed on a cathde ray tube or the like. If the reproduction means form part of a zerographic or photographic device, copies may be received, reconstructed and reproduced at some remote location.
Scanners of the above type can assume an unwieldy form if no attempt is made to compact the optical path and enable the scanner carriage (or electronic camera) to traverse in close proximity to the platen. This could be achieved, for example, with the aid of a super wide field, close up or fish eye lens. Alternatively, suitably mounted mirrors situated at each end of the carriage path may reflect the beam back and forth in such a manner as to maintain a constant lens-to-subject distance, independent of the position of the carriage. The first system involves an elaborate and expensive lens and still may be unwieldy, while the latter system involves an elongated optical path, limited by lens aperture and which is susceptible to the effects of vibration and which in general increases the size of the mechanism.
A solution which provides the requisite compactness and ridigity involves a process of folding the light beam within the moving carriage itself. This beam folding process may be achieved through the agency of mirrors or a prism and if suitably oriented, several successive reflections may significantly condense an appreciable portion of the beam length. The beam folding process, however, is not without problems in that errors of alignment become compounded and remedial adjustments are less easily understood and tend to cause simultaneous changes between various axes.
The most typical embodiment as applied to electrophotocopiers and the like requires, in addition to focal adjustment, the ability to shift the lens barrel and to tilt mirrors. Where the lens, mirrors and CCD form an integral sub-assembly, such a method imposes time consuming and exacting requirements.
Systems have been made where the lens barrel and CCD form an integral sub-assembly slidably mounted to move transversely on an appropriate deck surface, thereby permitting the lens/CCD sub-assembly to be manipulated so that the image of the document being copied may be projected upon the CCD sensitive area. However, this arrangement leaves something to be desired since the rays may be expected to pass obliquely through the lens system even for relatively minor error connection and may lead to vignetting and distortions due to curvilinear and other lens aberrations.
The system of adjustments embodied in the instant invention permits the ray path to remain substantially on the axis of the lens, permits a relaxation or elimination of separate mirror adjustments and yet attains the desired subject-to-CCD image reciprocity. Where the light path is folded by multiple mirror reflections, the angular relationship of individual ray paths, at the input pupil of the lens follows the same angular relationship as it would had the system comprised an unfolded ray arrangement, i.e. the rays coming directly from the illuminated subject with the same subject-to-pupil distance without the intervening mirrors.
More specifically, if the distance in respect of a non-mirrored system was, for example, 30 cm., then if the lens were constrained to follow a radial path of 30 cm. the rays would remain substantially upon the axis of the lens even if the lens were swung through a significant angle. This is analagous to a photographer moving his camera to one side but maintaining the same distance to the subject and then rotating the camera to again face the subject.
In order to extend and enhance this property associated with the radial path, if the origin of the generating radius be, for example, 2/3 of the cited 30 cm., namely 20 cm., the angular accommodating property would be influenced only to a minor degree, however. In addition to the angular remedial adjustment an accommodation to lateral subject displacement may be incorporated.
The selection of an optimum radius for fore-and-aft in contrast to side-to-side movement must be addressed to different objectives. For example, a loss of definition across the copy (side-to-side movement) as opposed to a loss of illumination due to the subject area being outside the projected fiber optic light swath.
Accordingly, the instant invention isolates the various components of adjustment and enables the scanner system to be aligned accurately without a repetitious back-tracking process as is usually required.